The formation of nanometer-sized structures remains a challenge that limits advances in many fields of nanotechnology such as fabrications of semiconductor integrated circuits (ICs), photonic band gap materials and magnetic storage devices. Emerging candidates to address the need for smaller features are ArF immersion lithography and extreme ultraviolet (EUV) lithography. E-beam lithography has further pushed the feature sizes down to sub 10 nm, but issues such as cost and low throughput still need to be addressed.
To date, several studies have reported block copolymer lithography by starting with a film of self-assembled poly(styrene-block-methyl methacrylate). In this system, one of the most common strategies to generate nanostructures in poly(styrene-block-methyl methacrylate) thin films is selective UV degradation and removal of poly(methyl methacrylate) microdomain. However, components of this block copolymer, polystyrene and poly(methyl methacrylate), have very low sensitivity to deep-UV and e-beam. Therefore, high irradiances are required to make nano-structured films.
Precise location of block copolymer patterns are performed only when a substrate is chemically or topographically modified, limiting the usefulness of this material in further patterning applications. Furthermore, this block copolymer cannot form small microdomains, which is also a crucial problem that limits development of block copolymer lithography.
Poly(α-methylstyrene-block-hydroxystyrene) has been used in block copolymer lithography. The poly(hydroxystyrene) block acts as a negative-tone photoresist and the second block made of poly(α-methylstyrene) can be selectively removed under UV irradiation in high vacuum conditions. However, multistep deep-UV irradiation and high vacuum conditions are required for selective removal of the poly(α-methylstyrene) block, which limits the usefulness of these materials in patterning processes.